bims-malgli Biomed News
on Biology of malignant gliomas
Issue of 2020‒11‒29
nineteen papers selected by
Oltea Sampetrean
Keio University

  1. Neurooncol Adv. 2020 Jan-Dec;2(1):2(1): vdaa134
      Background: Longitudinal tracking of tumor growth using noninvasive bioluminescence imaging (BLI) is a key approach for studies of in vivo cancer models, with particular relevance for investigations of malignant gliomas in rodent intracranial transplant paradigms. Akaluciferase (Akaluc) is a new BLI system with higher signal strength than standard firefly luciferase (Fluc). Here, we establish Akaluc BLI as a sensitive method for in vivo tracking of glioma expansion.Methods: We engineered a lentiviral vector for expression of Akaluc in high-grade glioma cell lines, including patient-derived glioma stem cell (GSC) lines. Akaluc-expressing glioma cells were compared to matching cells expressing Fluc in both in vitro and in vivo BLI assays. We also conducted proof-of-principle BLI studies with intracranial transplant cohorts receiving chemoradiation therapy.
    Results: Akaluc-expressing glioma cells produced more than 10 times higher BLI signals than Fluc-expressing counterparts when examined in vitro, and more than 100-fold higher signals when compared to Fluc-expressing counterparts in intracranial transplant models in vivo. The high sensitivity of Akaluc permitted detection of intracranial glioma transplants starting as early as 4 h after implantation and with as little as 5000 transplanted cells. The sensitivity of the system allowed us to follow engraftment and expansion of intracranial transplants of GSC lines. Akaluc was also robust for sensitive detection of in vivo tumor regression after therapy and subsequent relapse.
    Conclusion: Akaluc BLI offers superior sensitivity for in vivo tracking of glioma in the intracranial transplant paradigm, facilitating sensitive approaches for the study of glioma growth and response to therapy.
    Keywords:  Akaluc; bioluminescence imaging (BLI); glioblastoma (GBM); glioma; luciferase
  2. Trends Neurosci. 2020 Nov 21. pii: S0166-2236(20)30247-2. [Epub ahead of print]
      Glioblastoma the most aggressive form of brain cancer, comprises a complex mixture of tumor cells and nonmalignant stromal cells, including neurons, astrocytes, microglia, infiltrating monocytes/macrophages, lymphocytes, and other cell types. All nonmalignant cells within and surrounding the tumor are affected by the presence of glioblastoma. Astrocytes use multiple modes of communication to interact with neighboring cells. Extracellular vesicle-directed intercellular communication has been found to be an important component of signaling between astrocytes and glioblastoma in tumor progression. In this review, we focus on recent findings on extracellular vesicle-mediated bilateral crosstalk, between glioblastoma cells and astrocytes, highlighting the protumor and antitumor roles of astrocytes in glioblastoma development.
    Keywords:  astrocytes; crosstalk; exosomes; glioma; tumor microenvironment
  3. Neurooncol Adv. 2020 Jan-Dec;2(1):2(1): vdaa132
      Background: Fusion genes form as a result of abnormal chromosomal rearrangements linking previously separate genes into one transcript. The FGFR3-TACC3 fusion gene (F3-T3) has been shown to drive gliomagenesis in glioblastoma (GBM), a cancer that is notoriously resistant to therapy. However, successful targeting of F3-T3 via small molecular inhibitors has not revealed robust therapeutic responses, and specific targeting of F3-T3 has not been achieved heretofore. Here, we demonstrate that depleting F3-T3 using custom siRNA to the fusion breakpoint junction results in successful inhibition of F3-T3+ GBMs, and that exosomes can successfully deliver these siRNAs.Methods: We engineered 10 unique siRNAs (iF3T3) that specifically spanned the most common F3-T3 breakpoint with varying degrees of overlap, and assayed depletion by qPCR and immunoblotting. Cell viability assays were performed. Mesenchymal stem cell-derived exosomes (UC-MSC) were electroporated with iF3T3, added to cells, and F3-T3 depletion measured by qPCR.
    Results: We verified that depleting F3-T3 using shRNA to FGFR3 resulted in decreased cell viability and improved survival in glioma-bearing mice. We then demonstrated that 7/10 iF3T3 depleted F3-T3, and importantly, did not affect levels of wild-type (WT) FGFR3 or TACC3. iF3T3 decreased cell viability in both F3T3+ GBM and bladder cancer cell lines. UC-MSC exosomes successfully delivered iF3T3 in vitro, resulting in F3-T3 depletion.
    Conclusion: Targeting F3-T3 using siRNAs specific to the fusion breakpoint is capable of eradicating F3T3+ cancers without toxicity related to inhibition of WT FGFR3 or TACC3, and UC-MSC exosomes may be a plausible vehicle to deliver iF3T3.
    Keywords:  FGFR3-TACC3; RNAi; fusion genes; glioblastoma; precision medicine
  4. Cell Death Dis. 2020 Nov 21. 11(11): 998
      Isocitrate dehydrogenases (IDH1/2) are central molecular markers for glioblastoma. Providing in vitro or in vivo models with mutated IDH1/2 can help prepare facilities to understand the biology of these mutated genes as glioma markers, as well as help, improve therapeutic strategies. In this review, we first summarize the biology principles of IDH and its mutations and outline the core primary findings in the clinical context of neuro-oncology. Given the extensive research interest and exciting developments in current stem cell biology and genome editing, the central part of the manuscript is dedicated to introducing various routes of disease modeling strategies of IDH mutation (IDHMut) glioma and comparing the scientific-technological findings from the field using different engineering methods. Lastly, by giving our perspective on the benefits and limitations of patient-derived and donor-derived disease modeling respectively, we aim to propose leading research questions to be answered in the context of IDH1 and glioma.
  5. Sci Rep. 2020 Nov 26. 10(1): 20651
      Gliomas are currently classified through integration of histology and mutation information, with new developments in DNA methylation classification. However, discrepancies exist amongst the major classification methods. This study sought to compare transcriptome-based classification to the established methods. RNAseq and microarray data were obtained for 1032 gliomas from the TCGA and 395 gliomas from REMBRANDT. Data were analyzed using unsupervised and supervised learning and other statistical methods. Global transcriptomic profiles defined four transcriptomic glioma subgroups with 91.4% concordance with the WHO-defined mutation subtypes. Using these subgroups, 168 genes were selected for the development of 1000 linear support vector classifiers (LSVC). Based on plurality voting of 1000 LSVC, the final ensemble classifier confidently classified all but 17 TCGA gliomas to one of the four transcriptomic profile (TP) groups. The classifier was validated using a gene expression microarray dataset. TP1 cases include IDHwt, glioblastoma high immune infiltration and cellular proliferation and poor survival prognosis. TP2a is characterized as IDHmut-codel, oligodendrogliomas with high tumor purity. TP2b tissue is mostly composed of neurons and few infiltrating malignant cells. TP3 exhibit increased NOTCH signaling, are astrocytoma and IDHmut-non-codel. TP groups are highly concordant with both WHO integrated histology and mutation classification as well as methylation-based classification of gliomas. Transcriptomic profiling provides a robust and objective method to classify gliomas with high agreement to the current WHO guidelines and may provide additional survival prediction to the current methods.
  6. Methods Mol Biol. 2021 ;2236 157-175
      We will first describe analysis of MDSC subsets from patient tumors with multicolor flow cytometry. The key components of this methodology are to obtain viable single cell suspensions and eliminate red blood cell contamination.
    Keywords:  CyTOF; Flow cytometry; Glioblastoma (GBM); Immune analysis; Myeloid-derived suppressor cells (MDSCs); Patient tumor; Peripheral blood
  7. Acta Neuropathol Commun. 2020 Nov 23. 8(1): 201
      TERT promoter mutations are commonly associated with 1p/19q codeletion in IDH-mutated gliomas. However, whether these mutations have an impact on patient survival independent of 1p/19q codeletion is unknown. In this study, we investigated the impact of TERT promoter mutations on survival in IDH-mutated glioma cases. Detailed clinical information and molecular status data were collected for a cohort of 560 adult patients with IDH-mutated gliomas. Among these patients, 279 had both TERT promoter mutation and 1p/19q codeletion, while 30 had either TERT promoter mutation (n = 24) or 1p/19q codeletion (n = 6) alone. A univariable Cox proportional hazard analysis for survival using clinical and genetic factors indicated that a Karnofsky performance status score (KPS) of 90 or 100, WHO grade II or III, TERT promoter mutation, 1p/19q codeletion, radiation therapy, and extent of resection (90-100%) were associated with favorable prognosis (p < 0.05). A multivariable Cox regression model revealed that TERT promoter mutation had a significantly favorable prognostic impact (hazard ratio = 0.421, p = 0.049), while 1p/19q codeletion did not have a significant impact (hazard ratio = 0.648, p = 0.349). Analyses incorporating patient clinical and genetic information were further conducted to identify subgroups showing the favorable prognostic impact of TERT promoter mutation. Among the grade II-III glioma patients with a KPS score of 90 or 100, those with IDH-TERT co-mutation and intact 1p/19q (n = 17) showed significantly longer survival than those with IDH mutation, wild-type TERT, and intact 1p/19q (n = 185) (5-year overall survival, 94% and 77%, respectively; p = 0.032). Our results demonstrate that TERT promoter mutation predicts favorable prognosis independent of 1p/19q codeletion in IDH-mutated gliomas. Combined with its adverse effect on survival among IDH-wild glioma cases, the bivalent prognostic impact of TERT promoter mutation may help further refine the molecular diagnosis and prognostication of diffuse gliomas.
    Keywords:  1p/19q codeletion; CDKN2A; Glioma; IDH1/2; TERT
  8. Nanoscale. 2020 Nov 25.
      Intratumoral drug delivery is a promising approach for the treatment of glioblastoma multiforme (GBM). However, drug washout remains a major challenge in GBM therapy. Our strategy, aimed at reducing drug clearance and enhancing site-specific residence time, involves the local administration of a multi-component system comprised of nanoparticles (NPs) embedded within a thermosensitive hydrogel (HG). Herein, our objective was to examine the distribution of NPs and their cargo following intratumoral administration of this system in GBM. We hypothesized that the HG matrix, which undergoes rapid gelation upon increases in temperature, would contribute towards heightened site-specific retention and permanence of NPs in tumors. BODIPY-containing, infrared dye-labeled polymeric NPs embedded in a thermosensitive HG (HG-NPs) were fabricated and characterized. Retention and distribution dynamics were subsequently examined over time in orthotopic GBM-bearing mice. Results demonstrate that the HG-NPs system significantly improved site-specific, long-term retention of both NPs and BODIPY, with co-localization analyses showing that HG-NPs covered larger areas of the tumor and the peri-tumor region at later time points. Moreover, NPs released from the HG were shown to undergo uptake by surrounding GBM cells. Findings suggest that intratumoral delivery with HG-NPs has immense potential for GBM treatment, as well as other strategies where site-specific, long-term retention of therapeutic agents is warranted.
  9. Biochem J. 2020 Nov 27. pii: BCJ20200710. [Epub ahead of print]
      Glioblastoma (GBM) is the most aggressive brain cancer and its relapse after surgery, chemo and radiotherapy appears to be led by GBM stem cells (GSLCs). Also, tumor networking and intercellular communication play a major role in driving GBM therapy-resistance. Tunneling Nanotubes (TNTs), thin membranous open-ended channels connecting distant cells, have been observed in several types of cancer, where they emerge to drive a more malignant phenotype. Here, we investigated whether GBM cells are capable to intercommunicate by TNTs. Two GBM stem-like cells (GSLCs) were obtained from the external and infiltrative zone of one GBM from one patient. We show, for the first time, that both GSLCs, grown in classical 2D culture and in 3D-tumor organoids, formed functional TNTs which allowed mitochondria transfer. In the organoid model, recapitulative of several tumor's features, we observed the formation of a network between cells constituted of both Tumor Microtubes (TMs), previously observed in vivo, and TNTs. In addition, the two GSLCs exhibited different responses to irradiation in terms of TNT induction and mitochondria transfer, although the correlation with the disease progression and therapy-resistance needs to be further addressed. Thus, TNT-based communication is active in different GSLCs derived from the external tumoral areas associated to GBM relapse, and we propose that they participate together with TMs in tumor networking.
    Keywords:  cancer; cell communication; glioblastoma; stem cells; tunneling nanotubes
  10. Nat Metab. 2020 Nov 23.
      Inhibiting glycolysis remains an aspirational approach for the treatment of cancer. We have previously identified a subset of cancers harbouring homozygous deletion of the glycolytic enzyme enolase (ENO1) that have exceptional sensitivity to inhibition of its redundant paralogue, ENO2, through a therapeutic strategy known as collateral lethality. Here, we show that a small-molecule enolase inhibitor, POMHEX, can selectively kill ENO1-deleted glioma cells at low-nanomolar concentrations and eradicate intracranial orthotopic ENO1-deleted tumours in mice at doses well-tolerated in non-human primates. Our data provide an in vivo proof of principle of the power of collateral lethality in precision oncology and demonstrate the utility of POMHEX for glycolysis inhibition with potential use across a range of therapeutic settings.
  11. Clin Cancer Res. 2020 Nov 25.
      PURPOSE: Dexamethasone, a uniquely potent corticosteroid, is frequently administered to patients with brain tumors to decrease tumor-associated edema, but limited data exist describing how dexamethasone affects the immune system systemically and intratumorally in patients with glioblastoma (GBM), particularly in the context of immunotherapy.EXPERIMENTAL DESIGN: We evaluated the dose-dependent effects of dexamethasone when administered with programmed cell death 1 (PD-1) blockade and/or radiotherapy in immunocompetent C57BL/6 mice with syngeneic GL261 and CT-2A GBM tumors. Clinically, the effect of dexamethasone on survival was evaluated in 181 patients with isocitrate dehydrogenase (IDH) wild-type GBM treated with PD-(L)1 blockade, with adjustment for relevant prognostic factors.
    RESULTS: Despite the inherent responsiveness of GL261 to immune checkpoint blockade, concurrent dexamethasone administration with anti-PD-1 therapy reduced survival in a dose-dependent manner. Concurrent dexamethasone also abrogated survival following anti-PD-1 therapy with or without radiotherapy in immune-resistant CT-2A models. Dexamethasone decreased T-lymphocyte numbers by increasing apoptosis, in addition to decreasing lymphocyte functional capacity. Myeloid and natural killer cell populations were also generally reduced by dexamethasone. Thus, dexamethasone appears to negatively affect both adaptive and innate immune responses. As a clinical correlate, a retrospective analysis of 181 consecutive patients with IDH wild-type GBM treated with PD-(L)1 blockade revealed poorer survival among those on baseline dexamethasone. Upon multivariable adjustment with relevant prognostic factors, baseline dexamethasone administration was the strongest predictor of poor survival [reference, no dexamethasone; <2 mg HR, 2.16; 95% confidence interval (CI), 1.30-3.68; P = 0.003 and ≥2 mg HR, 1.97; 95% CI, 1.23-3.16; P = 0.005].
    CONCLUSIONS: Our preclinical and clinical data indicate that concurrent dexamethasone therapy may be detrimental to immunotherapeutic approaches for patients with GBM.
  12. J Cell Sci. 2020 Nov 26. pii: jcs.247189. [Epub ahead of print]
      A lack of biological markers has limited our ability to identify the invasive cells responsible for Glioblastoma multiforme. To become migratory and invasive, cells must down regulate matrix adhesions, which could be a physical marker of invasive potential. Murine astrocytes were engineered with common GBM mutations, e.g. Ink4a (Ink) or PTEN deletion and expressing a constitutively active EGF receptor truncation (i.e. EGFRvIII), to elucidate their effect on adhesion. While loss of Ink or PTEN did not affect adhesion, counterparts expressing EGFRvIII were significantly less adhesive. EGFRvIII reduced focal adhesion size and number, and these cells with more labile adhesions displayed enhanced migration. Regulation appears dependent not on physical receptor association to integrins but rather on the receptor's kinase activity resulting in transcriptional integrin repression. Interestingly, EGFRvIII intrinsic signals can be propagated by cytokine crosstalk to wildtype EGFR cells, resulting in reduced adhesion and enhanced migration. These data identify potential intrinsic and extrinsic mechanisms that gliomas use to invade surrounding parenchyma.
    Keywords:  Adhesion; Cancer; Extracellular matrix; Invasion
  13. Expert Rev Neurother. 2020 Nov 21.
      INTRODUCTION: Children with high-grade gliomas (pHGGs) represent a clinical population in substantial need of new therapeutic options given the inefficacy and toxicity of current standard-of-care modalities. Although immunotherapy has emerged as a promising modality, it has yet to elicit a significant survival benefit for pHGG patients. While preclinical studies address a variety of underlying challenges, translational clinical trial design and management also need to reflect the most updated progress and lessons from the field.AREAS COVERED: The authors will focus our discussion on the design of clinical trials, the management of potential toxicities, immune monitoring, and novel biomarkers. Clinical trial design should integrate appropriate patient populations, novel and preclinically optimized trial design, and logical treatment combinations, particularly those which synergize with standard of care modalities. However, there are caveats due to the nature of immunotherapy trials, such as patient selection bias, evidenced by the frequent exclusion of patients on high-dose corticosteroids. Robust immune-modulating effects of modern immunotherapy can have toxicities. As such, it is important to understand and manage these, especially in pHGG patients.
    EXPERT OPINION: Adequate integration of these considerations should allow us to effectively gain insights on biological activity, safety, and biomarkers associated with benefits for patients.
    Keywords:  biological correlates; clinical trial design; diffuse intrinsic pontine glioma; diffuse midline glioma; high-grade glioma; immunotherapy; toxicity
  14. Neurooncol Adv. 2020 Jan-Dec;2(1):2(1): vdaa124
      Background: Receptor tyrosine kinases such as epidermal growth factor receptors (EGFRs) and their downstream signaling pathways such as the Ras-Raf-mitogen-activated protein kinase (MAPK) pathway play important roles in glioblastoma (GBM). This study investigated the safety, pharmacokinetics, and efficacy of sorafenib (Ras/Raf/MAPK inhibitor) in combination with erlotinib (EGFR inhibitor) for treatment of recurrent GBMs.Methods: Patients with recurrent GBM were eligible. A novel sequential accrual trial design was used, where patients were sequentially accrued into separate treatment arms in phase I and phase II investigations to optimize recruitment efficiency. In phase I, a standard 3 + 3 format was used to identify dose-limiting toxicities (DLTs), determine maximum tolerated dose (MTD), and investigate pharmacokinetics. Phase II followed a 2-stage design with the primary endpoint being 6-month progression-free survival (PFS6).
    Results: Sixteen patients were recruited for phase I, and the MTD was determined to be sorafenib 200 mg twice daily and erlotinib 100 mg once daily. DLTs include Grade 3 hypertension, Grade 3 elevated liver transaminases, and Grade 4 elevated lipase. While erlotinib did not affect sorafenib levels, sorafenib reduced erlotinib levels. In phase II, 3 of 19 stage 1 participants were progression free at 6 months. This did not meet the predetermined efficacy endpoint, and the trial was terminated.
    Conclusion: This study identified the MTD and DLTs for sorafenib and erlotinib combination therapy for recurrent GBMs; however, efficacy data did not meet the primary endpoint. This study also demonstrates the feasibility of a novel sequential accrual clinical trial design that optimizes patient recruitment for multiarm studies, which is particularly effective for multicenter clinical trials.
    Keywords:  erlotinib; glioblastoma; molecular therapy; novel trial design; sorafenib
  15. Brain Pathol. 2020 Nov 26. e12921
      Diffuse gliomas are aggressive brain tumors that respond poorly to immunotherapy including immune checkpoint inhibition. This resistance may arise from an immunocompromised microenvironment and deficient immune recognition of tumor cells due to low mutational burden. The most prominent genetic alterations in diffuse glioma are mutations in the isocitrate dehydrogenase (IDH) genes that generate the immunosuppressive oncometabolite D-2-hydroxyglutarate. Our objective was to explore the association between IDH mutation and presence of cells expressing the immune checkpoint proteins galectin-9 and/or T-cell immunoglobulin and mucin-domain containing-3 (TIM-3). Astrocytic gliomas of World Health Organization (WHO) grades III or IV (36 IDH-mutant and 36 IDH-wildtype) from 72 patients were included in this study. A novel multiplex chromogenic immunohistochemistry panel was applied using antibodies against galectin-9, TIM-3, and the oligodendrocyte transcription factor 2 (OLIG2). Validation studies were performed using data from The Cancer Genome Atlas (TCGA) project. IDH mutation was associated with decreased levels of TIM-3+ cells (P < 0.05). No significant association was found between galectin-9 and IDH status (P = 0.10). Most TIM-3+ and galectin-9+ cells resembled microglia/macrophages, and very few TIM-3+ and/or galectin-9+ cells co-expressed OLIG2. The percentage of TIM-3+ T cells was generally low, however, IDH-mutant tumors contained significantly fewer TIM-3+ T cells (P < 0.01) and had a lower interaction rate between TIM-3+ T cells and galectin-9+ microglia/macrophages (P < 0.05). TCGA data confirmed lower TIM-3 mRNA expression in IDH-mutant compared to IDH-wildtype astrocytic gliomas (P= 0.013). Our results show that IDH mutation is associated with diminished levels of TIM-3+ cells and fewer interactions between TIM-3+ T cells and galectin-9+ microglia/macrophages, suggesting reduced activity of the galectin-9/TIM-3 immune checkpoint pathway in IDH-mutant astrocytic gliomas.
    Keywords:  Glioma; TIM-3; galectin-9; immune checkpoint; immunohistochemistry; isocitrate dehydrogenase; microglia; multiplex
  16. JCI Insight. 2020 Nov 24. pii: 144619. [Epub ahead of print]
      Glioblastoma multiforme (GBM) is a fatal human cancer in part because GBM stem cells are resistant to therapy and recurrence is inevitable. Previously, we demonstrated Zika virus (ZIKV) targets GBM stem cells and prevents death of mice with gliomas. Here, we evaluated the immunological basis of ZIKV-mediated protection against GBM. Introduction of ZIKV into the brain tumor increases recruitment of CD8+ T and myeloid cells to the tumor microenvironment. CD8+ T cells are required for ZIKV-dependent tumor clearance, as survival benefits are lost with CD8+ T cell depletion. Moreover, while anti-PD1 antibody therapy alone moderately improves tumor survival, when co-administered with ZIKV, survival increases. ZIKV-mediated tumor clearance also results in durable protection against syngeneic tumor re-challenge, which also depends on CD8+ T cells. To address safety concerns, we generated an immune-sensitized ZIKV strain, which is effective alone or in combination with immunotherapy. Thus, oncolytic ZIKV treatment can be leveraged by immunotherapies, which may prompt combination treatment paradigms for adult GBM patients.
    Keywords:  Brain cancer; Cancer immunotherapy; Immunology; Oncology
  17. Sci Rep. 2020 Nov 24. 10(1): 20492
      Maximal safe tumor resection remains the key prognostic factor for improved prognosis in brain tumor patients. Despite 5-aminolevulinic acid-based fluorescence guidance the neurosurgeon is, however, not able to visualize most low-grade gliomas (LGG) and infiltration zone of high-grade gliomas (HGG). To overcome the need for a more sensitive visualization, we investigated the potential of macroscopic, wide-field fluorescence lifetime imaging of nicotinamide adenine dinucleotide (NADH) and protoporphyrin IX (PPIX) in selected human brain tumors. For future intraoperative use, the imaging system offered a square field of view of 11 mm at 250 mm free working distance. We performed imaging of tumor tissue ex vivo, including LGG and HGG as well as brain metastases obtained from 21 patients undergoing fluorescence-guided surgery. Half of all samples showed visible fluorescence during surgery, which was associated with significant increase in PPIX fluorescence lifetime. While the PPIX lifetime was significantly different between specific tumor tissue types, the NADH lifetimes did not differ significantly among them. However, mainly necrotic areas exhibited significantly lower NADH lifetimes compared to compact tumor in HGG. Our pilot study indicates that combined fluorescence lifetime imaging of NADH/PPIX represents a sensitive tool to visualize brain tumor tissue not detectable with conventional 5-ALA fluorescence.
  18. Neurooncol Adv. 2020 Jan-Dec;2(1):2(1): vdaa138
      Background: RAS effector signaling pathways such as PI3K/mTOR and ERK are frequently dysregulated in glioblastoma. While small molecule targeted therapies against these pathways have appeared promising in preclinical studies, they have been disappointing in clinical trials due to toxicity and de novo and adaptive resistance. To identify predictors of glioblastoma sensitivity to dual pathway inhibition with mTORC1/2 and MEK inhibitors, we tested these agents, alone and in combination, in a cohort of genomically characterized glioblastoma cell lines.Methods: Seven genomically characterized, patient-derived glioblastoma neurosphere cell lines were evaluated for their sensitivity to the dual mTORC1/2 kinase inhibitor sapanisertib (MLN0128, TAK-228) alone or in combination with the MEK1/2 inhibitor trametinib (GSK1120212), using assessment of proliferation and evaluation of the downstream signaling consequences of these inhibitors.
    Results: Sapanisertib inhibited cell growth in neurosphere lines, but induced apoptosis only in a subset of lines, and did not completely inhibit downstream mTOR signaling via ribosomal protein S6 (RPS6). Growth sensitivity to MEK inhibitor monotherapy was observed in a subset of lines defined by loss of NF1, was predicted by an ERK-dependent expression signature, and was associated with effective phospho-RPS6 inhibition. In these lines, combined MEK/mTOR treatment further inhibited growth and induced apoptosis. Combined MEK and mTOR inhibition also led to modest antiproliferative effects in lines with intact NF1 and insensitivity to MEK inhibitor monotherapy.
    Conclusions: These data demonstrate that combined MEK/mTOR inhibition is synergistic in glioblastoma cell lines and may be more potent in NF1-deficient glioblastoma.
    Keywords:  MEK inhibitor; MTOR inhibitor; glioblastoma; neurosphere; targeted therapy